[1][3] From March 2008 to January 2009, Sun was temporary deputy secretary of the Zhangdian District Committee of the city of Zibo, Shandong.

According to The Washington Post, Sun's first engagement after being appointed as ambassador to Singapore was a meeting with a group of Singaporean Chinese-language online outlets.

According to an editor present at the meeting, Sun urged them to avoid reporting sensitive topics such as human rights issues in Xinjiang and Tibet, and that they should tell positive stories about China.

On 16 August 2022, following Speaker of the United States House of Representatives Nancy Pelosi's visit to Taiwan on 2 August 2022, Sun issued a statement stating that the visit "not only violates the U.S. own official one China principle, infringes on China's sovereignty, but also threatens the whole region's stability" and will not "allow this unprovoked challenge to our sovereignty pass without appropriate responses.

Sun helped organize Chief Executive of Hong Kong John Lee Ka-chiu's visit to Singapore in July 2023.